I. Field of the Invention
This invention relates in general to a ski binding and, specifically, to an inertia compensated ski binding which releasably binds a skier's boot to his ski and functions to cancel the forces generated by acceleration of the boot mass.
II. Description of the Prior Art
Ski bindings are designed to releasably hold a skier's boot to his ski with sufficient force to enable the skier to adequately control his skis while at the same time allowing the skier's boot to be released from the ski should the forces acting on his leg become great enough to injure him. The releasable ski binding which holds the skier's boot to the ski must allow for release of the skier's boot in the horizontal plane, including moments which tend to twist the skier's leg.
A popular type of ski binding is the so-called "step-in" binding in which the toe of the boot engages a rotatable toe-unit and the heel of the boot engages a releasably latched heel-unit. The rotatable toe-unit releases the boot from the ski by rotating about its pivot until release occurs. The rotatable toe-unit is held against rotation by adjustable spring loaded stops that prevent rotation until the moment resulting from the toe of the boot acting laterally on the toe-unit exceeds the preload. Most modern ski bindings provide a certain amount of toe-unit rotation before release occurs; this is done so that short duration impacts do not cause release. The force acting on the binding must exceed the preload long enough to allow the boot to travel through this distance before release occurs. Thus, a moment acting on the rotatable toe-unit having a pulse height and pulse width exceeding the predetermined shock work absorption capacity of the ski binding will automatically result in a release of the ski boot, whether or not significant leg forces are present.
Dynamic accelerations resulting from short duration impacts while skiing are usually referred to as "shock" by those skilled in the art of releasable ski bindings--the ability of a ski binding to not release prematurely because of "shock" is referred to as its "anti-shock capability". In this document, the term acceleration will be used instead of "shock" when referring to the time rate of change of velocity.
It has been established that there are two significant sources of force that act on ski bindings to cause release; these are the external leg forces involved in directing the ski, and the internal acceleration force resulting from the acceleration of the boot mass. Since these two forces are additive and can exist simultaneously, premature release of a binding during aggressive skiing can occur without a fall or the skier being in danger of injury because of the dynamic accelerations of the boot mass. The competitive skier is at greater risk of leg injury than the recreational skier because of the larger accelerations induced by high speed aggressive skiing on compacted surfaces. To prevent premature binding release the competitive skier increases the moment preload of the toe-unit, sometimes beyond that which his legs can sustain. When the competitive skier has a twisting fall where large acceleration are not present, the binding preload is too high for the leg forces alone to cause boot release and the skier's leg is injured.
A new type of ski binding has been developed which eliminates the internal acceleration forces acting to release the ski binding. U.S. Pat. No. 4,129,245 discloses a "plate-type" acceleration compensated device for ski bindings which comprises a pivot member adapted to engage a portion of a plate to which the ski boot is attached. The pivot member is pivotally carried such that the boot plate engaging portion of the pivot member is on one side of the pivot, and a mass connected to the pivot member is on the other side of the pivot. The mass is sized and positioned on the pivot member to generate a moment at the pivot equal and opposite to the moment generated by the boot mass during lateral or vertical acceleration of the boot to thereby eliminate acceleration as a factor in boot release. A shortcoming of "plate-type" ski bindings is the loss of feel of the skis caused by the "plate" between the boot and the ski; because of this shortcoming, the "plate-type" ski binding is used very little today. U.S. Pat. No. 4,277,084 discloses an acceleration compensated step-in ski binding that includes a pivotable toe-unit mounted on a support plate attached to the ski which engages the boot on one side of a first pivot and carries a mass on the opposite side of the first pivot. The mass is sized and positioned to generate a moment equal and opposite to the moment generated by lateral acceleration of the boot mass to eliminate lateral acceleration as a factor in boot release. The binding further includes a toe-cup assembly (for engaging the boot toe) that is coupled to the pivotable body member with a second pivot and parallel links that allow the toe-cup assembly to translate across the ski, under the influence of external lateral forces, without rotating. This assures that the effective fulcrum length between the first pivot axis and the boot mass is constant, to maintain the proper functioning of the acceleration compensating mechanism, despite the variability of the location at which the ski boot can contact the toe-cups. A shortcoming of this invention is that all the ski boot forces are imposed on the first pivot, requiring the first pivot to be strong enough to carry these large forces and precludes short fulcrum length between the pivot axis and the toe cup assembly. Additionally, ice can accumulate on the parallel link and interfere with proper release of the boot from the ski.